Organizational Unit:

School of Physics

Permanent Link

https://hdl.handle.net/1853/70755

Parent Organization

Organizational Unit

College of Sciences

Includes Organization(s)

Organizational Unit

Center for Relativistic Astrophysics

Organizational Unit

Mourigal Lab

ArchiveSpace Name Record

https://finding-aids.library.gatech.edu/agents/corporate_entities/156

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Publication Search Results

Now showing 1 - 10 of 22

Including a Warm Corona within the Inner Accretion Disk of Active Galactic Nuclei

(Georgia Institute of Technology, 2022-05) Xiang, Xin

Warm coronae, Comptonizing regions of warm (temperature kT ∼ 1keV), and optically thick (Thomson depth ∼ 10 - 20) gas, at the surfaces of accretion disks in active galactic nuclei (AGNs), have been proposed to explain the origin of the soft X-ray excess commonly observed in the X-ray spectra of AGNs. We calculate the X-ray emission from an irradiated constant density accretion disk atmosphere that includes heating from a warm corona, as well as illumination from an external X-ray power-law radiation, and blackbody emission from the dissipation in the accretion disk. The model accounts for the radial dependence of disk ionization, including the effects of light-bending on the illuminating X-rays. The final spectra are produced by integrating the local reflection/emission spectrum from approximately 2 to 400 gravitational radii. We demonstrate how the soft excess in AGN X-ray spectra depends on the warm corona parameters, including the heating fraction and optical depth, and the strength of the X-ray illumination. The model will be publicly released in 2022 for use in fitting AGN spectra.
Frustrated Magnetism and Searching For Quantum Spin Liquid Phases in Novel Materials

(Georgia Institute of Technology, 2018-05) Bender, Darian Marie

In my research, I wish to classify and identify a possible Quantum Spin-Liquid (QSL) phase on novel quantum materials. Materials of interest include the two triangular lattice materials, Li4CoTeO6 and Li4NiTeO6, in which Ni and Co ions with effective spin-1 and spin-1/2 each occupy a triangular lattice. We performed thermodynamic and magnetization measurements which indicate a possible exotic magnetic ground-state in both materials. We then performed elastic neutron scattering, providing additional evidence for exotic magnetism in these materials. Inelastic neutron scattering measurements are still necessary to probe the nature of the magnetic correlations and to confirm a QSL phase. Another material of interest is the kagomé lattice material, KFe3(OH)6(SO4)2 (known as Fe-Jarosite). This material is a popular QSL.1, 2 Small crystals of Fe-Jarosite have been created by hydrothermal synthesis in Mourigal Lab, and preliminary measurements of magnetization are in good agreement with known values.1, 3 Neutron scattering is required to study this material’s spin-dynamics, however, scattering is weak. Therefore, further synthesis attempts must be performed in order to increase the size of single-crystals of Fe-Jarosite from 2.6 mm to 1.0 cm.
Generation and Stability of Charged Toroidal Droplets

(Georgia Institute of Technology, 2018-05) Aizenman, Aaron

In this project, we have determined the quantitative parameters governing the transition phases of charged toroidal droplets. An instability reminiscent of the Saffman-Taylor Instability (viscous fingers) has been observed when toroidal droplets are exposed to a significantly high voltage source, but this is the only recorded development of this instability in a three-dimensional situation (Alberto Fernandez-Nieves 2016). We created a silicon oil environment of extremely high viscosity with aminopropyl terminated silicon oil (ATSO) added to lower surface tension. We utilized surfactants to minimize the surface tension between the inner and outer fluids to slow down the dynamics of the system enough to give the surface a chance to reach equipotential, thus allowing us to test the theories that currently exist in the field. In an attempt to disprove the possibility that this was the Saffman-Taylor Instability, we also attempted viscosity inversion experiments. These failed, thus giving us almost conclusive proof that this was indeed the Saffman-Taylor Instability. By proving that this is indeed the Saffman-Taylor Instability, we have also proven that this three-dimensional problem can be analyzed as a series of two-dimensional problems. This approach vastly simplifies further calculations and analysis of similar systems. A secondary focus of this project was to perfect a method of automated generation of inherently unstable shapes in viscoelastic materials. By using a novel method of 3D printing, the project attempted to increase the efficiency with which we can generate samples for testing and observation while also adding uniformity and consistency to the trials and experiments.
Model Selection in Gravitational Wave Astronomy

(Georgia Institute of Technology, 2017-12) Napier, Katherine

The several detections of gravitational waves by the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo detector are providing insights about the nature of gravity in our Universe [1]. As the number of detected gravitational waves increases, it will be necessary to employ computationally inexpensive methods to extract the parameters of the gravitational wave sources. This proof of concept study utilizes principal component analysis (PCA) to try to reduce the number of vectors needed to describe binary black hole (BBH) parameter space. The results of this study suggest that performing PCA on face-on BBH systems, those at zero degrees inclination, adds an unnecessary level of complexity. However, PCA is a beneficial method to apply to waveforms that are morphologically complex such as those from edge-on BBH systems, those at 90 degrees inclination. Running PCA on a catalog of specific waveforms in one area of parameter space can inform how to construct waveforms in other regions of parameter space. If these waveforms can be constructed to a high level of accuracy using only a few principal components (PCs), it will significantly reduce the computational cost associated with generating template waveforms. Instead of creating a waveform template for every parameter combination, the PCs can be used to construct waveforms from similar areas of parameter space.
Bayesave Analysis Study on Recovering Waveform Complexity through Reconstructions

(Georgia Institute of Technology, 2017-05) Day, Brian M.

The field of gravitational wave astronomy is a means of observing the universe in a new way. Crucial to the success of this new astronomy is analyzing the data obtained from the Laser Interferometer Gravitational-Wave Observatory (LIGO). Gravitational waves are oscillations of spacetime that propagate to Earth. We can predict these waveforms using solutions of Einstein’s Equations from general relativity. There are several ways the LIGO scientific collaboration uses to detect signals. This thesis presents my work on one such method, Bayeswave analysis. Bayeswave analysis is one tool to process the data collected from the detectors. Bayeswave offers analysis on a potential event that is agnostic, in other words it is independent of theoretical predictions of the signal, due to it being a minimal assumption analysis and can be used to determine if the event is a signal, a glitch, or noise. Through the analysis, Bayeswave uses evidence values obtained from comparing signal, glitch, and noise models to determine what the event most likely is and produces reconstructions of both the signal and glitch models. This information can be used to further understand the event in the data. Although Bayeswave has shown to be able to accurately reconstruct simple waveforms, its ability to accurately reconstruct waveforms from systems with more complex initial parameters is not known. Therefore, this study is to determine if Bayeswave can accurately reconstruct known injected signals with varied initial parameter complexity. The ability for Bayeswave to reconstruct the more complex injected waveforms is gauged by analyzing the median overlap between the reconstruction and the injection as a function of signal-to-noise ratio (SNR), which is a gauge of how strong the signal is compared to background noise, for various inclination angles, the strain and frequency data as functions of time, and the residual strain of the reconstruction waveform when it is subtracted from the injected waveform as a function of time.
Ultra-Close Tidal Disruption Events with Prompt Hyperaccretion

(Georgia Institute of Technology, 2015-08-18) Evans, Christopher

A bright flare from a galactic nucleus followed at late times by a t^-5/3 decay in luminosity is often considered to be the signature of a tidal disruption of a star by a massive black hole. The flare and afterglow are produced when the stream of stellar debris released by the disruption returns to the vicinity of the black hole, self-intersects, and eventually forms an accretion disk or torus. In the canonical scenario of a solar-type star disrupted by a 10^6 solar mass black hole, the time between the disruption of the star and the formation of the accretion torus could be years. Presented here are fully general relativistic simulations of a new class of tidal disruption events involving ultra-close encounters of solar-type stars with intermediate mass black holes. In these encounters, a thick disk forms promptly after disruption, on timescales of hours. After a brief initial flare, the accretion rate remains steady and highly super-Eddington for a few days at approximately 100 solar masses per year.
Star-Disk Collisions in the Galactic Center

(Georgia Institute of Technology, 2015-08-18) Kieffer, Thomas F.

Recent observations of the Galactic Center (GC) have revealed that there is a relative paucity of Red Giant (RG) stars within the central parsec. However, these observations conflict with our current theoretical understanding. We would expect the GC to have formed a segregated cusp of late-type stars. A recent explanation for this theoretical issue is that the outer envelopes of RG stars may have been stripped due to collisions with a fragmenting accretion disk in the GC. Both numerical and analytic models of star-disk collisions have been considered by several authors prior to this work, but a majority of the literature has focused on either the envelope stripping of a Main-Sequence (MS) star or other phenomena associated with this particular interaction. Here we investigate the envelope stripping of a RG star of radius R* = 10 R and mass M* = 1M colliding with the dense regions of a fragmenting disk. From our simulations, we are able to conclude that a RG star is likely to be stripped of its outer envelope and, occasionally, disrupted.
Reduced Model for Gravitational Wave Sources

(Georgia Institute of Technology, 2015-08-18) Maganazertuche, Lorena

One of the most interesting and exotic systems in the universe is a system of two black holes. When black holes orbit each other, they will eventually collide, forming a single black hole with a mass less than the sum of the two initial masses. This missing ``mass," up to ten percent, is converted into gravitational waves (GW) making these systems one of the most energetic in the universe. In the last decade, numerical simulations of the coalescence of binary black hole spacetimes have become a possibility and have since then progressed. Each simulation, with a unique set of initial parameters, constructs a gravitational wave signal, also called a waveform. In this work, I study the modeling of the radiated energy of non-precessing and precessing systems as functions of the binary system' s initial parameters. Because constructing a template bank of these waveforms remains computationally intensive, the next step is to introduce the use of Principal Component Analysis (PCA), which will efficiently capture the essential features over a large parameter space of the simulations. It acts on collections of waveforms to find bulk features such as the energy and momentum radiated. These features may provide the ``smoking gun" of mergers for gravitational wave burst detection.
A Study on Porous Silicon Gas Sensors: Metal Oxide Depositions to Organic Materials

(Georgia Institute of Technology, 2015-08-18) Lin, Arthur

This paper has two main topics. The first topics covers the detection of volatile organic compounds with porous silicon (PSi) sensors. The second part explores the possibility of using conducting polymers as coatings for the PSi sensors as a catalyst for CO and CO2 detection. Porous semiconductor materials have been sought after as volatile organic compound gas sensors due to their optical properties. However, the optical sensors have a major flaw in their inability to distinguish different gases. Additionally, optical porous semiconductor sensors are overly sensitive to environmental factors, demising their ability to be used in an industrial setting. Therefore, in this project, we seek to explore methods using conductometric porous silicon sensors, potentially solving the drawbacks of optical sensors. Additionally, we seek to use the data collected during this period to construct a better understanding of the interaction of gases and porous semiconductor materials, expanding on the inverse hard/soft acid/base theory. Another flaw of porous semiconductor sensors is that they rely on the competing precesses of chemisorption and physisorption. If a gas is both physically and chemically inert, then the sensor will fail to detect the gas. However, certain polymers have the capability of acting as a catalyst, triggering electron exchange between the gas and sensor, producing the signal needed for detection. Studies have shown polypyrrole as a effective catalyst for CO2 detection. We wish to combine that with metal oxide deposits for studying CO2 in the IHSAB model.
Particle Image Velocimetry of Collapsing Toroidal Droplets

(Georgia Institute of Technology, 2015-08-18) Berger, Eric M.

The goal of this study is to explore the mechanism by which unstable toroidal droplets collapse inwardly. As such, particle image velocimetry methods will be employed in obtaining an experimental picture of the velocity field inside of unstable toroidal droplets as they collapse. The inward collapse exhibited by unstable toroidal droplets is unique to the geometry of the torus and is therefore physically interesting. There is currently not an available experimental picture of this collapse, so this study will attempt to fill that void. Ultimately the results of this study will be compared against the currently accessible theoretical pictures of collapsing toroidal droplets, leading to further refinements in the field.